The clinical role of endocardial catheter recording and mapping is to direct ablation, surgical, and drug therapies in the treatment of supraventricular tachycardia, ventricular tachycardia, atrial flutter, atrial fibrillation and other arrhythmias. The success and advancement of current therapies is dependent upon the development and use of more precise localization techniques which will allow accurate anatomical determination of abnormal conductive pathways and other arrhythmogenic sites. Historically, the electrophysiologist has had to compromise between placing the catheter in the place of greatest clinical interest and areas which are anatomically accessible.
Open heart surgery to perform electrophysiological recording and mapping has largely been supplanted by cardiac catheterization performed under local anesthesia in the electrophysiology lab. Prior art catheter placement has been generally restricted to areas which can be repeatedly accessed by the electrophysiologist. These areas include the HRA (high right atrium), the RVA (right ventricular apex), the RVOT (right ventricular outflow tract), the coronary sinus and the HIS bundle. To obtain meaningful information about additional placement sites, the number of electrograms recorded over a given area may be increased, and the precise position of the electrode array of the distal tip portion of the catheter may be varied. Some of these additional sites include atrial sites above the tricuspid and mitral valves, ventricular sites circumferential to the mitral and tricuspid valve leaflets, distal areas of the coronary sinus and great cardiac vein, the AV nodal area and the left ventricle, to name a few.
One area of advancement in improving localization techniques and accessing additional recording sites includes the use of steerable catheters. One type of prior art steerable catheter offers improved maneuverability to specific, otherwise inaccessible sites by providing catheters shaped specifically to access a particular site. Although perhaps useful for some less inaccessible sites, the use of this type of catheter is limited, not very practical, and not helpful in reaching sites requiring active articulation during placement. Three such pre-shaped catheters are described in U.S. Pat. Nos. 3,503,385 issued to Stevens, 3,729,008 issued to Berkovits, and 4,860,769 issued to Forgerty, each of which is incorporated herein by reference.
Another type of prior art steerable catheter attempts to improve placement maneuverability by providing catheters having deflecting tips. These catheters include a relatively soft and flexible distal tip portion of a certain length attached to a proximal shaft made from a relatively stiffer material. Generally, the tip may be selectively deflected but only in a prescribed arc, i.e., the tip bends in one planar direction, with the bend having a fixed, predetermined radius of curvature. Some examples of deflecting tip catheters are described in U.S. Pat. Nos. 4,920,980 issued to Jackowski, 4,960,411 issued to Buchbinder, and 4,960,134 issued to Webster, each of which is also incorporated herein by reference. In devices of this type, a pullwire attached to the distal tip portion at or near the tip is pulled proximally while the catheter shaft is restrained, thus causing the tip to deflect. Alternatively, the pullwire is restrained while the shaft portion is advanced distally, producing the same effect. Various means are known for causing the tip to bend in a predetermined plane and direction.
A disadvantage of the above-described preformed and deflecting tip type catheters is that the tip of the catheter in each case may be deflected or steered only in a prescribed configuration which cannot be altered during its placement. That is, the steerable tip has a radius of curvature which is fixed, thus restricting the accessibility of the distal tip to certain anatomical sites without additional significant efforts of the electrophysiologist maneuvering the catheter exteriorly of the patient, and some sites may not be accessible at all. Such excessive maneuvering of the catheter exteriorly of the patient is difficult, frustrating, time consuming and inefficient to the physician performing a delicate procedure, and is thus inherently more risky for the patient undergoing that procedure. Most serious is the increased exposure of the patient, physicians and technicians to dangerous X-ray radiation which is used for fluoroscopic examination during procedures of this type.
Many of the desired sites require that the catheter traverse paths having many sharp bends and be able to negotiate multiple changes of direction through any or all of the three perpendicular planes of movement. Four-way steerable catheters have been developed in an attempt to provide a catheter with the above-described multi-planar maneuverability. As examples, such four-way steerable catheters are described in U.S. Pat. Nos. 3,470,876 issued to Barchilon, and 4,921,482, 4,998,916 and 5,037,391 issued to Hammerslag, each of which is also incorporated herein by reference. While such four-way steerable catheters may be improvements over two-way steerable catheters of this general type, the four-way steerable devices similarly suffer the disadvantage that the tips can deflect in only one predetermined configuration, that is, having a fixed, predetermined radius of curvature.
As a result of the above described disadvantage of prior art steerable catheters, the electrophysiologist must obtain and maintain not one but a set of similar steerable electrode catheters for use during any single clinical evaluation of a patient. For example, the user will have on hand a catheter having a steerable tip having a small radius of curvature; another with a medium radius of curvature and a third with a relatively large radius of curvature. While this availability of differently radiused tips is beneficial, it is often not known by the electrophysiologist which size will be required at any given moment during a diagnostic or therapeutic intracardiac procedure. Moreover, similar tip placements may require different radiused tips from one individual to another, even those of the same general body size and mass. When it is discovered by the electrophysiologist that a catheter then placed in a patient has an incorrectly radiused tip for the required procedure, the catheter must be completely withdrawn from the patient (through whichever one of the femoral, subclavian, jugular or brachial approaches was used), and a new properly radiused electrode catheter tip must be reintroduced into the heart. This substitution may take up to two hours or more to complete, including the time required to precisely reposition the electrode tip.
Moreover, the initially selected, but improperly sized catheter must generally be discarded, never having been actually used for its intended purpose, as such devices are intended as "single use only" devices, for a variety of safety reasons. Steerable catheters are relatively expensive devices, and this waste of an otherwise good device is especially troublesome.
Deflectable catheter tips of the type just described are generally resiliently biased to some degree to return to a straight configuration when not acted upon by the various prior art mechanisms for causing tip deflection. Another drawback with such catheters, as a result of this resiliency, is the sometimes undesired tendency of the tip to return to an undeflected position, or to merely change the amount of deflection, during the course of the electrophysiological procedure.
Furthermore, it is frequently necessary to rotate the entire catheter tip portion by applying torque to the catheter shaft by rotating the entire control handle. Some prior art catheters include steering control mechanisms or actuators which are located at a single particular radial location on the control handle. In use, however, when such handles are rotated, the electrophysiologist often loses a degree of control over the device, as the steering control mechanism is rotated to some position which is less easily manipulated.